KR20150050715A

KR20150050715A - High hard multilayer sheet

Info

Publication number: KR20150050715A
Application number: KR1020130130731A
Authority: KR
Inventors: 박환석; 황덕율; 권동주; 이종훈; 신창학; 예성훈; 송예리; 유다영; 남해림
Original assignee: (주)엘지하우시스
Priority date: 2013-10-31
Filing date: 2013-10-31
Publication date: 2015-05-11
Also published as: WO2015064928A1; KR101800482B1; CN105705332A; CN105705332B; JP6524077B2; JP2016534898A

Abstract

(Meth) acrylic acid ester monomer, 75 to 88 parts by weight of a styrene monomer, 2 to 5 parts by weight of a styrene monomer, and 10 to 20 parts by weight of an N-substituted maleimide monomer, layer; And a polycarbonate layer comprising a polycarbonate copolymer.

Description

[0001] HIGH HARD MULTILAYER SHEET [0002]

The present invention relates to a high hardness multilayer sheet.

Recently, a variety of mobile devices have been popularized. At present, materials used in mobile devices should have excellent properties such as weather resistance, resistance to scratching with external stimuli, impact resistance against external impact, and workability.

As a raw material used in conventional mobile devices, a liquid crystal window using polymethylmethacrylate (PMMA) resin as a main material has excellent weather resistance and scratch resistance, but has a low impact resistance. Recently, the popularity of ultra- The disadvantages of conventional polymethylmethacrylate (PMMA) resins are becoming more widespread. In order to produce ultra-slim mobile devices, the thickness of the window of mobile devices has been reduced to about 0.5 mm, and various attempts have been made to reinforce the weakened impact resistance while removing various protective films to reduce the overall module thickness.

One embodiment of the present invention provides a high hardness multilayer sheet comprising a laminated structure of a polymethylmethacrylate layer and a polycarbonate layer.

Another embodiment of the present invention provides a high hardness multilayer sheet which is made by an extrusion process and which exhibits excellent physical properties, while optimizing the components of the polymethylmethacrylate layer and the polycarbonate layer.

In one embodiment of the invention, about 75 parts by weight to about 88 parts by weight of a (meth) acrylic acid ester monomer, about 2 to about 5 parts by weight of a styrene monomer, and about 10 to about 20 parts by weight of an N-substituted maleimide monomer A polymethyl methacrylate layer comprising an acrylic copolymer formed into a weight part; And a polycarbonate layer comprising a polycarbonate copolymer.

The thickness of the polymethylmethacrylate layer may be from about 40 um to about 70 um.

The glass transition temperature of the acrylic copolymer may be about 130 캜 to about 140 캜.

The weight average molecular weight of the acrylic copolymer may be about 100,000 to about 15.

The polymethylmethacrylate layer may further comprise about 0.1 to about 1.5 parts by weight of an antioxidant and about 0.5 to about 3.0 parts by weight of a UV stabilizer per 100 parts by weight of the acrylic copolymer.

The thickness of the polycarbonate layer may be from about 900 [mu] m to about 950 [mu] m.

The glass transition temperature of the polycarbonate copolymer may be from about 140 캜 to about 150 캜.

The melt index of the polycarbonate copolymer may be from about 3 to about 22.

About 0.3 to about 2.0 parts by weight of an antioxidant and about 0.5 to about 3.0 parts by weight of a UV stabilizer per 100 parts by weight of the polycarbonate copolymer.

The polymethylmethacrylate layer and the polycarbonate layer may be co-extruded.

And a hard coating layer on the polymethylmethacrylate layer or below the polycarbonate layer.

The high hardness multilayer sheet may have a pencil hardness of about 4H or more.

The warpage of the high hardness multilayer sheet may be about 0.1 mm or less after being left for 72 hours at a temperature of 85 캜 and a humidity of 85%.

The high-hardness multilayer sheet can have excellent dimensional stability and excellent scratch resistance.

Further, the high-hardness multilayer sheet is excellent in bending properties under high temperature and high humidity conditions and can be easily applied to various electronic products.

1 is a cross-sectional view of a high-hardness multilayer sheet according to an embodiment of the present invention.
2 is a cross-sectional view of a high-hardness multilayer sheet according to another embodiment of the present invention.
3 is a cross-sectional view of a high-hardness multilayer sheet according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Typically, tempered glass is applied to most mobile devices such as smart phones and tablet products. However, despite the advantages of tempered glass, plastic covers are increasingly demanded for plastic covers because they are advantageous in terms of breakdown characteristics, cost, process yield and so on compared with tempered glass.

In the plastic cover material, a component showing optical characteristics similar to tempered glass may be polymethyl methacrylate (hereinafter referred to as PMMA), polycarbonate (hereinafter referred to as PC), or the like. Generally, the PMMA has high scratch resistance and excellent optical properties, but has a limit in impact resistance. On the other hand, although the PC has excellent impact properties, it has a limitation on scratch resistance.

Therefore, there have been attempts to secure both a scratch property and an impact resistance characteristic by forming a PMMA layer on the surface layer and introducing a PC layer into the core, but a sheet made of other kinds of resins has been known to have scratch resistance, impact resistance, And there is a problem that the quality stability is not easy because the physical properties are very different according to the thickness of each layer and the content of the constituent components.

In order to solve the above problems, in one embodiment of the present invention, a copolymer comprising 75 parts by weight to 88 parts by weight of a (meth) acrylic acid ester monomer, 2 parts by weight to 5 parts by weight of a styrene monomer and 10 parts by weight of an N-substituted maleimide monomer A polymethylmethacrylate layer comprising an acrylic copolymer formed with 20 parts by weight; And a polycarbonate layer comprising a polycarbonate copolymer.

The high-hardness multilayer sheet can be produced by an extrusion process to optimize the constituent components of the polymethylmethacrylate layer and the polycarbonate layer to ensure excellent dimensional stability, and at the same time to have excellent anti-strike properties. Further, the high-hardness multilayer sheet is excellent in bending properties under high temperature and high humidity conditions and can be easily applied to various electronic products.

The polymethyl methacrylate layer

The polymethylmethacrylate layer (hereinafter referred to as PMMA layer) is prepared by mixing 75 parts by weight to 88 parts by weight of a (meth) acrylic acid ester monomer, 2 to 5 parts by weight of a styrene monomer, and 10 to 20 parts by weight of an N-substituted maleimide monomer Based on the weight of the acrylic copolymer.

The acrylic copolymer may contain an (meth) acrylic acid ester monomer, a styrene monomer, and an N-substituted maleimide monomer in a certain amount at the same time, thereby ensuring excellent heat resistance and securing superior bending properties at high temperature and high humidity.

Specifically, when the (meth) acrylic acid ester monomer is contained outside the above range, the durability of the acrylic copolymer can not be ensured. In addition, when the N-substituted maleimide monomer is included in an amount outside the above range, the glass transition temperature of the acrylic copolymer may be lowered to cause a problem of warpage due to a decrease in heat resistance.

When the styrene monomer is contained outside the above range, the PMMA layer can not secure physical properties such as scratch resistance and durability.

More specifically, the (meth) acrylic acid ester monomer is at least one monomer selected from the group consisting of methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, (Meth) acrylate, 2-ethylbutyl (meth) acrylate, and combinations thereof.

The N-substituted maleimide monomer is selected from the group consisting of N-phenylmaleimide, maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, But are not limited to, isobutyl maleimide, N-butyl maleimide, N-cyclohexyl maleimide, N-chlorophenylmaleimide, N-methylphenylmaleimide, N-bromophenylmaleimide, It may be at least one selected from the group consisting of maleimide, N-hydroxyphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide and N-benzylmaleimide.

The thickness of the PMMA layer may be from about 40 um to about 70 um. Since the thickness of the PMMA layer can be controlled by controlling the extrusion amount of the PMMA layer resin composition flowing into the feed block from the extruder, in order to maintain the thickness of the PMMA layer accurately, the amount of the introduced PMMA layer resin composition is always uniform So that it is necessary to accurately control the extrusion amount.

When the thickness of the PMMA layer is increased, scratch characteristics are improved but impact properties are decreased. In addition, when the thickness of the PMMA layer is reduced, the stress characteristics are reduced but the impact properties are improved. In general, both of them are in a trade off relationship. Therefore, by adjusting the thickness of the PMMA layer to be in the range of about 40 탆 to about 70 탆, it is possible to optimize the physical property balance with the polycarbonate layer by simultaneously ensuring the desired level of scratch characteristics and impact properties.

The glass transition temperature of the acrylic copolymer may be about 130 캜 to about 140 캜. If the glass transition temperature of the acrylic copolymer is less than about 130 ° C, durability may be limited under high temperature and high humidity conditions. If the glass transition temperature is more than about 140 ° C, color discoloration is severe and the polymethyl methacrylate layer is easily broken Lt; / RTI >

The weight average molecular weight of the acrylic copolymer may be about 100,000 to about 15. The weight average molecular weight means an average molecular weight obtained by averaging the molecular weight of the component molecular species of the polymer compound having a molecular weight distribution by a weight fraction. By maintaining the weight average molecular weight of the acrylic copolymer within the above range, the mechanical strength and the polycarbonate The mechanical strength and the bending property of the high-hardness multilayer sheet can be satisfactorily realized.

The antioxidant prevents cross-linking of polymers that may occur during discoloration and processing, maintains long-term physical properties of the PMMA layer, and prevents discoloration. Examples of the antioxidants include hindered phenols phenol, lactone, phosphite, thioester, and the like, but the present invention is not limited thereto.

For example, octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, tris (2,4-di-tert-butylphenyl) phosphite, tetrakis [methylene Butyl-4-hydroxyphenyl) propionate] methane, 4,4'-thiobis (6-tert-butyl-m-cresol), pentaerythrityl Tetrakis (3-laurylthiopropionate), and the like.

The antioxidant may include about 0.1 part by weight to about 1.5 parts by weight based on 100 parts by weight of the acrylic copolymer. By keeping the above range, the decomposition of the antioxidant can be suppressed and stable physical properties can be maintained.

The UV stabilizer serves to prevent aging phenomena such as cracking and discoloration caused by ultraviolet rays when the plastic is exposed to sunlight for a long time. Examples of the UV stabilizer include benzophenone, benzotriazole, HALS And the like can be mainly used, but the present invention is not limited thereto.

(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, poly [[6- (1,1,3,3-tetramethylbutyl) amino] -s-tri Azine-2,4-dinyl] [(2,2,6,6-tetramethyl-4-piperidinyl) imino] hexamethylene [2,2,6,6-tetramethyl-4-piperidinyl ) Imino]], dimethyl succinate and 4-hydroxy-2,2,6,6, -tetramethyl-1-piperidine ethanol and the like.

The UV stabilizer may include about 0.5 part by weight to about 3.0 parts by weight based on 100 parts by weight of the acrylic copolymer. By maintaining the above range, UV-induced discoloration can be effectively suppressed.

Polycarbonate layer

The polycarbonate layer (hereinafter, PC layer) may include a polycarbonate copolymer. The polycarbonate copolymer has no particular structural limitations and can be formed by interfacial polymerization or melt polymerization. For example, LUPOY PC 1201-08 (LG Chem) or LUPOY PC 1300-30 (LG Chem) may be used as the polycarbonate copolymer.

The thickness of the PC layer may be from about 900 [mu] m to about 950 [mu] m. The thickness of the PC layer can be controlled by controlling the extrusion amount of the PC layer resin composition flowing into the feed block from the extruder. In order to accurately maintain the thickness of the PC layer resin composition, It is necessary to accurately control the extrusion amount.

By controlling the thickness of the PC layer to the above range, it is suitable to maintain the mechanical strength of the high-hardness multilayer sheet.

The glass transition temperature of the polycarbonate copolymer may be from about 140 캜 to about 150 캜. If the glass transition temperature of the polycarbonate copolymer is less than about 140 ° C, the physical properties at high temperature and high humidity may be lowered. If the polycarbonate copolymer is more than about 150 ° C, the processing temperature may be increased.

The melt index of the polycarbonate copolymer may be from about 3 to about 22. Melt Folw Index (MI) refers to the melt flow index, which refers to the weight of a resin flowing through a capillary at a constant load and temperature for 10 minutes.

If the melt index of the polycarbonate copolymer is less than 3, the temperature of the extrusion process must be controlled to a high level due to the lowering of the flowability of the polycarbonate copolymer, and the difference in flow with the upper layer, PMMA layer, have. In addition, when the melt index exceeds 22, there may occur a problem that the sheet workability in a T-die is deteriorated when the polycarbonate copolymer is extruded.

About 0.3 to about 2.0 parts by weight of an antioxidant and about 0.5 to about 3.0 parts by weight of a UV stabilizer per 100 parts by weight of the polycarbonate copolymer. The matters relating to the antioxidant and the UV stabilizer are as described above.

Hardness Multilayer sheet

The polymethylmethacrylate layer and the polycarbonate layer may be co-extruded. Coextrusion refers to a method of making a coating film and sheet by using one or more extruders to add one or more layers during extrusion coating, film or sheet production. The co-extrusion process is not particularly limited, and the PMMA layer and the PC layer can be formed by a general co-extrusion process.

However, since the co-extrusion process is suitable for realizing physical properties to be realized by a high hardness multilayer sheet of a PMMA layer / PC layer structure, the PMMA layer realizes excellent scratch characteristics and appearance characteristics, it is possible to realize the toughness characteristic and the heat resistance, so that the physical properties of the high hardness sheet can be controlled as a whole.

And a hard coating layer on the polymethylmethacrylate layer or below the polycarbonate layer. Referring to FIGS. 2 and 3, the hard-coated multi-layer sheet 100 includes a hard coat layer (not shown) and a hard coat layer (not shown). The hard coat layer has a hard coat layer The PMMA layer 10 and the PC layer 20 or the hard coating layer 30, the PMMA layer 10, the PC layer 20 and the hard coating layer 30. [

For example, a urethane-based acrylate copolymer series may be used as a component of the hard coat layer. The urethane-based acrylate copolymer-based hard-coating resin is a resin prepared by copolymerization of an acrylic monomer having a hydroxy group and an isocyanate-reactive polyol and isocyanate. The urethane-based acrylate copolymer hard-coating resin is a polyether polyol, a polyester polyol, a polycaprolactone polyol, , Polybutadiene polyol, aromatic isocyanates such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI), or isophorone diisocyanate (IPDI), hexamethylene diisocyanate And HMDI (hexamethylene diisocyanate), so that an appropriate raw material having elasticity capable of three-dimensional molding and having an nas-crest capable of withstanding external stimuli can be selected and used.

Also, the thickness of the hard coat layer may be between about 5 um and about 30 um. When the thickness of the hard coating layer is less than 5 탆, there is a problem that the gloss of the film may change. When the thickness of the hard coating layer is more than about 30 탆, cracks may occur in the hard coating layer.

The hard coat layer may further contain an additive. Examples of the additive include a silicone additive (a reactive monomer / oligomer having a silicon group), a fluorine-based additive (a reactive monomer / oligomer having a fluorine group), a resin having a silicon group or a fluorine group, Oil, and the like.

Further, the hard coat layer may further contain a photoinitiator. Examples of the photoinitiator include benzene ketone, benzoin ethers, acetophenone derivatives, ketoxime ethers, benzophenone, (amino) benzoate, benzyl Dimethylketal compounds and at least one cationic initiator selected from onium salts, ferrocenium salts and diazonium salts, or a combination of the free radical initiator and the cation The initiator mixture may be used.

The high hardness multilayer sheet may have a pencil hardness of about 4H or more. Pencil hardness is the hardness of a material compared with the hardness of a pencil lead. It can be expressed by H, F, B, etc. according to hardness and concentration. The pencil hardness of the high-hardness multilayer sheet is measured using ASTM D3363-05 (Mitsubishi Pencil, 1 kg load). By maintaining the hardness of about 4H or more, an excellent hardness can be realized as compared with a normal multilayer sheet.

The plastic window material to which the high hardness multilayer sheet is applied is warped under the conditions of high temperature and high humidity, and such warping may cause problems in operation of the touch panel. Therefore, when a certain level of warpage occurs under high temperature and high humidity conditions, it can not be applied to a window cover for a touch panel. For example, the warpage of the high-hardness multilayer sheet may be about 0.1 mm after being left for 72 hours at a temperature of 85 캜 and a humidity of 85%.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto.

< Manufacturing example >

PMMA -1 (acrylic copolymer)

83 parts by weight of methyl methacrylate (MMA), 2 parts by weight of styrene, 15 parts by weight of N-cyclohexylmaleimide, 0.2 parts by weight of n-octylmercaptan as a chain transfer agent, and 0.2 parts by weight of azobisisobutyronitrile ) Was added to an aqueous solution of a dispersant (250 parts by weight of ion-exchanged water + 2 parts by weight of a polymerization dispersant), and the mixture was polymerized at 80 DEG C for 4 hours and further polymerized at 110 DEG C for 2 hours to remove residual monomer, Of PMMA-1 (acrylic copolymer) was prepared. The molecular weight of the PMMA-1 was 130,000 and the Tg was 132 占 폚.

PMMA -2 (acrylic copolymer)

PMMA-2 was prepared in the same manner as in PMMA-1, except that n-cyclohexylmaleimide was changed to phenylmaleimide in the process for producing PMMA-1. The molecular weight of the PMMA-2 was 120,000, and the Tg was 133 占 폚.

PMMA -3 (acrylic copolymer)

HP202 (LG MMA) having a molecular weight of 120,000 and a Tg of 104 占 폚 was used.

PC -1 (polycarbonate copolymer)

LUPOY PC 1201-08 (LG Chemical) having a melt index (300 캜, 1.2 kg) of 8.0 and a Tg of 148 캜 was used.

PC -2 (polycarbonate copolymer)

LUPOY PC 1300-30 (LG Chemical) having a melt index (300 DEG C, 1.2 kg) of 30 and a Tg of 144 DEG C was used.

< Example And Comparative Example >

Additives (antioxidant and UV stabilizer) were added to PMMA-1, PMMA-2 and PMMA-3 as shown in the following Table 1, and the PMMA layer resin composition was formed in a pellet form at 275 ° C through a twin screw extruder. Additives (antioxidants and UV stabilizers) were added to PC-1 and PC-2 as shown in the following Table 1, and PC layer resin compositions were formed in the form of pellets through a twin screw extruder at 275 ° C. Thereafter, the PMMA layer resin composition and the PC layer resin composition were co-extruded to prepare a high-hardness multilayer sheet including a PMMA layer and a PC layer. The thicknesses of the PMMA layer and the PC layer in the above Examples and Comparative Examples were measured using a Scanning Electronic Microscope (SEM).

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 P
M
M
A floor PMMA1 100 - 100 - 100 - 100 - PMMA2 - 100 - 100 - - - - PMMA3 - - - - - 100 - 100 additive 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 P
C layer PC1 100 100 100 100 - 100 - 100 PC2 - - - - 100 - 100 - additive 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 0.3 /
2.0 Layer thickness
(um)
(PMMA layer
/ PC layer) 980
(50 /
930) 975
(55 /
920) 980
(40 /
940) 980
(60 /
920) 980
(40 /
940) 980
(50 /
930) 940
(50
/ 890) 1000
(90
/ 910)

* Additive (parts by weight): Phenolic antioxidant (Irganox1010) / UV stabilizer (Hostavin B-CAP)

< Experimental Example > - Evaluation of properties of multilayer structure

1) Pencil hardness: The hardness of the above Examples and Comparative Examples were measured using ASTM D3363-05 (Mitsubishi Pencil, 1 kg load).

2-1) Initial warpage: The high-hardness multilayer sheet of the examples and comparative examples was prepared as a test piece having a width of 60 mm and a length of 100 mm, and the height of the edge and the bottom was measured. The degree of the upward finishing was measured using a gap gauge Respectively.

2-2) Late bending: The specimen of the high-hardness multilayer sheet was allowed to stand at a temperature of 85 ° C and a humidity of 85% for 72 hours, and the height between the edge and the bottom of the specimen was measured. (Gap gauge).

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Pencil hardness 4H 4H 4H 4H 2H 4H 4H 4H Initial bending
(mm) 0.04 0.05 0.05 0.05 0.04 0.08 0.10 0.12 Late bending
(mm) 0.09 0.10 0.07 0.09 0.11 0.20 0.18 0.17

Referring to Table 2, it can be confirmed that Examples 1 to 4 have higher hardness and better bending properties than Comparative Examples 1 to 4. Specifically, in Comparative Examples 1 and 3, a PC layer including a polycarbonate copolymer having a melt index of 22 or higher, and Comparative Examples 2 and 4 each including a PMMA layer including an acrylic copolymer having a glass transition temperature of less than 130 ° C Compared with Examples 1 to 4, which is a laminated structure of a PC layer including a PMMA layer containing an acrylic copolymer having a glass transition temperature of 130 ° C to 140 ° C and a polycarbonate copolymer having a melt index of 3 to 22, It was found that the hardness was lowered and the warpage property was also lowered.

In Comparative Example 3, the thickness of the PC layer was set to 900 μm or less, the relative bending property was lowered due to the increase in thickness of the PMMA layer, and the thickness of the PMMA layer was set to 70 μm or more in Comparative Example 4, It was confirmed that only the hardness was maintained and the warpage characteristics were lowered, so that it was confirmed that only the high hardness multilayer sheets of Examples 1 to 4 can realize the warpage property and the anti-stretch property simultaneously.

100: high-hardness multilayer sheet
10: Polymethyl methacrylate layer
20: polycarbonate layer
30: Hard coating layer

Claims

(Meth) acrylic acid ester monomer, 75 to 88 parts by weight of a styrene monomer, 2 to 5 parts by weight of a styrene monomer, and 10 to 20 parts by weight of an N-substituted maleimide monomer, layer; And
A laminate structure of a polycarbonate layer containing a polycarbonate copolymer
High hardness multilayer sheet.

The method according to claim 1,
The thickness of the polymethylmethacrylate layer is in the range of 40um to 70um
High hardness multilayer sheet.

The method according to claim 1,
The glass transition temperature of the acrylic copolymer is from 130 캜 to 140 캜
High hardness multilayer sheet.

The method according to claim 1,
The weight average molecular weight of the acrylic copolymer is 100,000 to 150,000
High hardness multilayer sheet.

The method according to claim 1,
Wherein the polymethylmethacrylate layer further comprises 0.1 to 1.5 parts by weight of an antioxidant and 0.5 to 3.0 parts by weight of a UV stabilizer per 100 parts by weight of the acrylic copolymer
High hardness multilayer sheet.

The method according to claim 1,
The thickness of the polycarbonate layer is from 900 [mu] m to 950 [mu] m
High hardness multilayer sheet.

The method according to claim 1,
The polycarbonate copolymer has a glass transition temperature of from 140 캜 to 150 캜
High hardness multilayer sheet.

The method according to claim 1,
The polycarbonate copolymer has a melt index of 3 to 22
High hardness multilayer sheet.

The method according to claim 1,
0.3 parts by weight to 2.0 parts by weight of an antioxidant and 0.5 to 3.0 parts by weight of a UV stabilizer per 100 parts by weight of the polycarbonate copolymer
High hardness multilayer sheet.

The method according to claim 1,
Wherein the polymethylmethacrylate layer and the polycarbonate layer are co-extruded to form
High hardness multilayer sheet.

The method according to claim 1,
Further comprising a hard coat layer on the polymethyl methacrylate layer or below the polycarbonate layer
High hardness multilayer sheet.

The method according to claim 1,
The hard multilayer sheet has a pencil hardness of 4H or more
High hardness multilayer sheet.

The method according to claim 1,
After leaving for 72 hours under the conditions of a temperature of 85 캜 and a humidity of 85%, the warpage of the high-hardness multilayer sheet
High hardness multilayer sheet.